In the wafer processing schemes used in the semiconductor industry, LPCVD reactors are generally hot wall, reduced pressure reactors that consist of a quartz tube heated by a furnace, typically comprising infrared heating elements, with pocess gas introduced into one end and pumped out to a vacuum pump at the other end. The LPCVD reactor tubes are sealed on the ends with cylindrical end caps through which all of the process gases flow. End caps are made to be removable so that the inside of the reactor tube may be serviced. Boats of wafers for processing are inserted through a door in one or the other of the end caps.
Pressures in the LPCVD reaction chamber are typically 0.25 to 2.0 torr (30 to 250 Pa) with temperatures ranging between 300.degree. and 700.degree. C. and even up to 1000.degree. C. and gas flows between 100 and 1000 std. cm.sup.3 /min. (sccm). The reactions of the gases at high temperatures and low pressures cause thin layers of materials with desirable properties to be deposited on the surface of silicon wafers placed within the LPCVD reactor.
Commercial LPCVD reactors mix the reaction gases at a mixing or control panel that is physically some distance from the reactor tube. This permits the use of only one gas line into the LPCVD reactor itself, thereby simplifying the number of connections to the end cap. However, attempts at using low vapor pressure liquid sources or gases that may react at very low temperatures in such systems have proven unsatisfactory because the gases tend to react and form by-products or are used up before they reach the reaction zone in the vicinity of the wafers. No doubt premature reaction of pre-mixed gases is a problem in any process where reaction gases are to be mixed and reacted.
Multiple gas injection systems have been proposed, however, they have always involved separate attaching, sealing and changing steps for each of the gas lines, which may number three, four or more, and separate apparatus for each gas input line. See, for example, U.S. Pat. No. 4,573,431 issued Mar. 4, 1986. Since all of these proposed systems were tied to the end cap of the LPCVD reactor tube, a considerable amount of additional work had to be performed on the gas lines during removal and attachment of the end cap.
It would be desirable if a technique or an apparatus could be devices which would permit these incoming gases to react only at the deposition zone. Such a system would permit increased process development flexibility. Preferably, such a system would also have a simple and a quick detachment mechanism for all of the incoming gas lines.